Radial piston hydraulic motors are well known in the art. Such radial piston hydraulic motors include a plurality of cylinders oriented in a radial direction relative to a central axis of the motor. In some conventional radial piston hydraulic motors, the cylinders are formed in a cylinder block to which an output shaft is connected. The cylinder block rotates within a housing having an undulating inner cam surface. Each cylinder receives a piston assembly provided with a roller at its radially outer end that engages the undulating cam surface of the housing. During operation, hydraulic fluid pressure forces the pistons radially outward and this causes the rollers to roll over the undulating surface. Reactionary forces act on the cylinder block and cause it and the output shaft to rotate.
Other conventional radial piston hydraulic motors include an output shaft that is mounted on a centrally located eccentric cam. A plurality of piston-cylinder assemblies are located radially outwardly of the eccentric cam with one surface of either the piston or the cylinder engaging the eccentric cam. Hydraulic fluid pressure provided to a chamber within each cylinder acts on the piston to cause relative movement between the piston and the cylinder. The relative movement between the piston and the cylinder results in a force being applied to the eccentric cam by the engaging surface. This force causes rotation of the eccentric cam and thus rotation of the output shaft.